Natural Selection

Question 1

What are the three types of natural selection?

Answer 1

• Directional Selection
• Stabilising Selection
• Disruptive Selection

Question 2

What is directional selection?

Answer 2

Directional Selection occurs when one extreme phenotype is favoured over the other extreme

Question 3

What is Disruptive Selection?

Answer 3

Where both extremes of the range of phenotypes are selected over the intermediate types (e.g. very small and very large beaks are favoured over medium beaks)

Question 4

What is stabilising selection?

Answer 4

When the intermediate phenotype is selected over extreme phenotypes. Occurs when the environment hasn’t changed much.

Question 5

What is selection?

Answer 5

a process in which environmental or genetic influences determine which types of organism thrive better than others

Question 6

What is speciation?

Answer 6

When a new species develops as a result of two groups of the same species becoming reproductively isolated and adapting to different environments

Question 7

What are the characteristics of ‘a species?’

Answer 7

• Similar in morphology, behaviour, biochemistry, ecological niche.
• Can breed to produce fertile offspring, but not with other species.
• Shares a common ancestor

Question 8

A population has been separated by a river and can not mix. How do new species evolve? 6 marks

Answer 8

Geographical isolation
Separate gene pools so no interbreeding
Variation due to mutation
Different selection pressures/ abiotic factors/ habitats
Different reproductive success/ selected organisms survive and reproduce
Leads to change in allele frequency

Question 9

A population of trees in an alpine forest evolved adaptations to their mountain environment. Use your knowledge of selection to explain how.

Answer 9

Variation in original colonisers / mutations took place
resulting in some better adapted for survival and having a greater reproductive success so the allele frequencies changed